The Replacement Theory
by blinnn
Summary: Truman may not be as dumb as he looks. My Valentine's Day Gift for RoseGarden! Happy Valentine's Day! : Hope you like it!


Author's Note!: Hey there everyone! This is a one-shot! Its written for the fabulous Rosegarden! She's my valentine from Dasey Nation. I hope you enjoy your "Well written Trashy/Dasey fic that you didn't get for the x-mas exchange!" haha. SO READ AWAY PEOPLE. The idea kind of just came to me while I was driving... and day dreaming.. not a great combination. haha :) ENJOY NOW.

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**The Replacement Theory**

A Life with Derek Fanfiction

**Disclaimer:** I don't own Life with Derek.

_Is she talking to me? I'm honestly not paying any attention to her..._ he thought dully as his attention turned to the other tables around the restaurant. Casey was rambling again and he really never listened to her once she got started. His eyes roamed past her and spotted other couples that were also on their dates. After scanning the couple right behind Casey, he glanced to the left and saw a table of three girls. They were undoubtedly friends enjoying a fun, sporadic evening with each other.

The three girls all had blonde hair, but all had different colored eyes. One with blue eyes, one with brown, and one with green. _Which one to choose?_ He contemplated. It looks like he wouldn't have to make the decision because the brown-eyed girl looked back at him, smiling flirtatiously.

His body visibly stiffened thinking of a response that was subtle enough to make sure his girlfriend wouldn't notice.

_Girlfriend..._ he thought before quickly looking back to where Casey was sitting. Noticing that she was no longer there, he looked around nervously.

"Casey?" He spoke, hardly loud enough for her to hear him, wherever she was. _Did she see me looking at those other girls and leave?_

"Don't worry." The brown eyed blonde spoke to his confused form, "She said she was going to the bathroom." _How did she hear Casey, but he didn't? Women must be on an entirely different brain frequency._

Relaxing a bit, he smirked at the girl.

"I'm Samantha." She smiled, extending her arm to him discreetly.

"Truman." He responded, taking her hand in his and bringing it to his lips for a quick peck.

Recently he'd realized just exactly what kind of relationship he and Casey had. It was possibly the most open relationship he'd ever been in without it actually being spoken of. He didn't think that Casey knew just how open it was. She never saw any other guys, _well..._ she never went on dates with them, kissed them, done much more with them. He, on the other hand, did. He almost didn't even try to be discreet about it. She probably knew all about his escapades, but she'd never break up with him. She _needed_ him, way more than he needed her. Frankly, he was doing her a favor by cheating on her every chance he got. If she had to be the one to _tell_ him that she didn't _actually_ have feelings for him... well lets just say she'd beat herself up about it for hours before she got the nerve to speak to him. She never was one to let people down.

Things had been getting out of hand, as of late. They'd been losing their _flair_, their _edge_. When they started dating, things were always a challenge. They fought about mostly anything but it was fun, at least. Now, he just found it easier to agree with whatever she said, because she usually didn't care enough to put all of her effort into their arguments. It just wasn't worth it for him. What can he say? He got bored.

"Don't you think your girlfriend will be mad if she finds you flirting with someone else?" She asked, but he's _positive_ she doesn't care either way.

"She's used to it." Truman replied swiftly and Samantha raised her eyebrows.

"I see..." She started, glancing up to see Casey emerging from the bathrooms, "well I think you dropped your napkin." She finished, winking as she handed it to him as if she picked it up from the floor.

He turned it over quickly to see, 'Call me - 555-1790.' Placing it in his pocket, Casey returned to her seat.

"So, I was thinking we could go back to my house and watch a movie. What do you think?" Casey offered.

"Sure." He agreed, trying to sound enthused.

Casey accepted his answer, without a smile. _Maybe he didn't give her enough credit._ Maybe she knew that things were getting bland. She _had_ to know, its just so obvious. He just assumed that she was always too preoccupied by other... _thoughts_ to realize the difference.

* * *

She picked the movie, _again._ He didn't bother to argue, because he didn't really plan on paying attention to it. _Boy was he wrong._ Did they silently decide that they weren't going to kiss each other anymore? He began to wonder if they were even dating. Of course, he'd never _ask. _

So the rom-com was halfway through and Casey was clutching a tissue to her chin, just in case she needed it._ Bored out of his mind, _that's what he was feeling.

When the credits started rolling, Casey gathered her used tissues to throw them away. He just sat on the couch, waiting for Casey's OCD to cease. He was just staring blankly, replaying some of the scenes from the movie in his head. It was just the video though, he couldn't for the life of him remember what was going on. _Not that he cared to. _He just sat there, thoughtfully fingering the napikin in his pocket.

"Why is that?" He heard her ask. _When did she sit back down?_ And **what** is she talking about?

"What?" He asked. She huffed; she knew he wasn't listening, _again._

"I said, you've been acting weird lately. Why is that?" He heard her this time. She didn't sound completely hurt by his change of behavior; more _curious_ than worried.

"What do you mean, 'different'?" He wondered. He's not going to admit anything that didn't have to.

"Well, when we first started dating... we were always, you know, fun." She started, a frown forming on her dace, "But now you just seem so uninterested." She finished.

Truman's mind ventured to the first time he had realized just exactly what it was Casey McDonald wanted from him.

* * *

_"Casey are you trying to pick a fight with me?" He asked, almost sounding disappointed;__** almost**._

_"I don't have to try! You give me reason after reason for me to fight with you. I'm just finally calling you out on it!" She replied._

_"Hey, Spacey. Keep it down, will ya?" a voice had sounded from up the stairs. "Some people are trying to tune you out."_

_"Der-ek! This is **not** the time." She yelled back to him._

_"Geesh, someone's cranky!" Derek's voice was heard again._

_She rolled her eyes before turning back to Truman. "As I was saying... give me on good reason why I shouldn't break up with you right now?"_

_"Casey, you don't really want to do that. Please..." He started to beg, it wasn't something he normally did, but he wasn't done with her yet, it wasn't over till he said its over._

_"I'll give you a reason, Case." Casey turned around to see a smirking Derek on their staircase. Her eyes lit with fire, never had he seen her so passionate about something; even if it was out of anger._

_Her jaw clenched as she glared at him, "Go away, Derek. This doesn't concern you."_

_"You won't break up with him because you need someone there for you at all times. Whether you want him or not, that's not the point. The point is that you need a companion, and you definitely won't get that from anyone else." He sneered darkly at her._

_If Truman wasn't staring intently at Casey's face, he wouldn't have noticed the millisecond of hurt that flashed across her face. _But he was... and he did.

_"How Ironic; you are the one with a different girl every night." Casey argued._

_"There's a difference between being popular," he gestured to himself, "and being _desperate_." He finished, gesturing to her._

_Truman just watched in fascination as the two step-siblings advanced towards each other. When they were literally about three inches away from each other, Derek spoke, "I'm outta here."_

_With that, he was gone. Truman hadn't noticed before, but Derek was sporting a gym bag the whole time._

_Casey's breathing evened out before Truman decided to break in."Where was Derek going with his gym bag? Hockey Practice?" He asked._

_"No. Derek's going to his mom's house for the rest of the rest of the week. Thankfully." Casey said, unconvincingly. Truman nodded as to say he understood._

_"Ugh. Can you believe him?! I can't believe him!" She started to rant. _Maybe he shouldn't have mentioned Derek again.

_He sighed. _Wrong move, buddy. _She glared at him, hearing his 'remark'. "You have something to say?" She provoked._

_"Casey, please. Don't start fighting with me again. It's fun when its not serious."_

_"You're the one who had to complain. You know what? You are just like Derek, and since I'm going to live in peace of **him** for the rest of the week, maybe it'd be in your best interests for **you **to stay clear of me, too." She spoke sternly._

_"Fine." He gave up, striding over towards the door._

_"Don't bother calling me, either." She told him getting closer than usual to him. There was something else going on. Something different, he couldn't quite put his finger on-  
_

_And just like that, she was kissing him. _What?!_ He couldn't understand how she went so fast from hating his guts to a full-on make-out session in her foyer._

_When they broke for air, he decided to find out what was going on. "Case? Wha-?" Was all that he got out._

_"Shh." She put her finger to his mouth, "I need this." She told him, and he could sense the desperation in her voice, her features, everything about her._

_So he kissed her back, with more force than ever before._

_That's when he realized it: the fighting was a thrill for her. He **was** just like Derek. Except... he **wasn't** Derek; he never would be... and he knew that's what she wanted him to be.

* * *

_"We're actually really talking about this, now?" Truman asked, amazed.

"Yeah, well... we've been tip-toeing around the subject for a long time... so..." Casey answered.

A thought occurred to Truman at that very moment: Derek was gone once again. The school hockey team was on a celebratory trip to Winnipeg, again. He'd already been gone for almost a week, which meant he'd be home later that night. Casey must be _really_ wound up. What a strong correlation. Every time Derek was gone for an extended period of time, Casey started something. The difference was, Truman wasn't having it this time.

"I'm not the only one that's uninterested." Truman mumbled loud enough for her to hear. He had a plan, and he wasn't backing down.

"What's that supposed to mean?!" She asked, her voice displaying confusion mixed with a bit of repulsion. _Okay more than a bit._

"If you don't know, you're crazier than I thought you were." He answered; a gasp was emitted from her mouth.

"First I'm not interested, and now I'm crazy? What's your issue?!" She responded to his insult. _Just as planned._

"I'm tired of you using me for your sick fantasy, Casey. Get yourself the real thing... I'm out." He said, getting up from his spot on the couch but waiting for Casey's rebuttal, knowing she'd want an explanation.

_Was she really this dense?_

"I'm sorry if you think I'm 'using you'," She started sarcastically, "but at least I'm not flirting and doing who knows what else with other people behind your back." She stated.

He let out a bitter laugh. "You might as well be!" He responded.

Her eyes went wide in disbelief. "Excuse me?! Just because you do it does mean everyone does. God, even Derek has better sense than to go through with cheating." She said.

He chuckled darkly at her reply. _Of course, _it always comes back to _him_. "I'm not Derek!" He yelled, and it seemed to affect her because she looked as if she were getting dizzy. She held the back of her hand up to her forehead. "I'm sorry, okay? As much as I try, I can never be what you really want! I'm tired of you expecting me to act exactly like _him_! I'm leaving. I'm calling Samantha, who I met at the restaurant tonight while you were in the bathroom... and you don't have to worry about me cheating on you anymore, because we're no longer together." He spoke, gesturing between the two of them. He then traveled to the door and opened it up to reveal Derek about to do the same thing.

Truman glanced back to Casey one last time, "I hope you get what you really want, Casey... even if you may not know what it is." His parting words stung her, and her eyes welled up with tears; a few trickling down her cheeks.

Derek watched Truman's retreating form in confusion, "What was all that about?" He asked before noticing her tears.

His eyes widened and he immediately dropped his luggage in the doorway, striding over to her.

"Uh... Case? You okay?" He winced, trying not to look at the swelling in her eyes. His hands were resting on her shoulders for comfort.

She looked at him, the tears had ceased. She saw the sincerity in his eyes, hidden behind the discomfort. _He cared._

"I will be." She said, taking each side of his face in her hands and closing the distance between them.

The kiss was wet, due to Casey's recent crying fit; but it was _something._

At first, he was still, unmoving, confused... but as soon as her mouth started moving against his, he gave up the fight. _Which wasn't too hard._ Sliding his hands down her arms, he snaked his arms around her waist as her's made their way around his neck.

Derek wasn't really sure what was going on, but he definitely didn't mind. He and Casey were _kissing_ and as wrong as some may say it was, it felt so _damn _right. _So he wasn't going to mess with that._


End file.
